/**
 * @file
 * SNMP input message processing (RFC1157).
 */

/*
 * Copyright (c) 2006 Axon Digital Design B.V., The Netherlands.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * Author: Christiaan Simons <christiaan.simons@axon.tv>
 */

#include "lwip/opt.h"

#if LWIP_SNMP /* don't build if not configured for use in lwipopts.h */

#include "lwip/ip_addr.h"
#include "lwip/mem.h"
#include "lwip/udp.h"
#include "lwip/stats.h"
#include "lwip/snmp.h"
#include "lwip/snmp_asn1.h"
#include "lwip/snmp_msg.h"
#include "lwip/snmp_structs.h"

#include <string.h>

/* public (non-static) constants */
/** SNMP v1 == 0 */
const s32_t snmp_version = 0;
/** default SNMP community string */
const char snmp_publiccommunity[7] = "public";

/* statically allocated buffers for SNMP_CONCURRENT_REQUESTS */
struct snmp_msg_pstat msg_input_list[SNMP_CONCURRENT_REQUESTS];
/* UDP Protocol Control Block */
struct udp_pcb* snmp1_pcb;

static void snmp_recv(void* arg, struct udp_pcb* pcb, struct pbuf* p, struct ip_addr* addr, u16_t port);
static err_t snmp_pdu_header_check(struct pbuf* p, u16_t ofs, u16_t pdu_len, u16_t* ofs_ret, struct snmp_msg_pstat* m_stat);
static err_t snmp_pdu_dec_varbindlist(struct pbuf* p, u16_t ofs, u16_t* ofs_ret, struct snmp_msg_pstat* m_stat);


/**
 * Starts SNMP Agent.
 * Allocates UDP pcb and binds it to IP_ADDR_ANY port 161.
 */
void
snmp_init(void)
{
	struct snmp_msg_pstat* msg_ps;
	u8_t i;

	snmp1_pcb = udp_new();

	if(snmp1_pcb != NULL) {
		udp_recv(snmp1_pcb, snmp_recv, (void*)SNMP_IN_PORT);
		udp_bind(snmp1_pcb, IP_ADDR_ANY, SNMP_IN_PORT);
	}

	msg_ps = &msg_input_list[0];

	for(i = 0; i < SNMP_CONCURRENT_REQUESTS; i++) {
		msg_ps->state = SNMP_MSG_EMPTY;
		msg_ps->error_index = 0;
		msg_ps->error_status = SNMP_ES_NOERROR;
		msg_ps++;
	}

	trap_msg.pcb = snmp1_pcb;
	/* The coldstart trap will only be output
	   if our outgoing interface is up & configured  */
	snmp_coldstart_trap();
}

static void
snmp_error_response(struct snmp_msg_pstat* msg_ps, u8_t error)
{
	snmp_varbind_list_free(&msg_ps->outvb);
	msg_ps->outvb = msg_ps->invb;
	msg_ps->invb.head = NULL;
	msg_ps->invb.tail = NULL;
	msg_ps->invb.count = 0;
	msg_ps->error_status = error;
	msg_ps->error_index = 1 + msg_ps->vb_idx;
	snmp_send_response(msg_ps);
	snmp_varbind_list_free(&msg_ps->outvb);
	msg_ps->state = SNMP_MSG_EMPTY;
}

static void
snmp_ok_response(struct snmp_msg_pstat* msg_ps)
{
	err_t err_ret;

	err_ret = snmp_send_response(msg_ps);

	if(err_ret == ERR_MEM) {
		/* serious memory problem, can't return tooBig */
	} else {
		LWIP_DEBUGF(SNMP_MSG_DEBUG, ("snmp_msg_event = %"S32_F"\n", msg_ps->error_status));
	}

	/* free varbinds (if available) */
	snmp_varbind_list_free(&msg_ps->invb);
	snmp_varbind_list_free(&msg_ps->outvb);
	msg_ps->state = SNMP_MSG_EMPTY;
}

/**
 * Service an internal or external event for SNMP GET.
 *
 * @param request_id identifies requests from 0 to (SNMP_CONCURRENT_REQUESTS-1)
 * @param msg_ps points to the assosicated message process state
 */
static void
snmp_msg_get_event(u8_t request_id, struct snmp_msg_pstat* msg_ps)
{
	LWIP_DEBUGF(SNMP_MSG_DEBUG, ("snmp_msg_get_event: msg_ps->state==%"U16_F"\n", (u16_t)msg_ps->state));

	if(msg_ps->state == SNMP_MSG_EXTERNAL_GET_OBJDEF) {
		struct mib_external_node* en;
		struct snmp_name_ptr np;

		/* get_object_def() answer*/
		en = msg_ps->ext_mib_node;
		np = msg_ps->ext_name_ptr;

		/* translate answer into a known lifeform */
		en->get_object_def_a(request_id, np.ident_len, np.ident, &msg_ps->ext_object_def);

		if(msg_ps->ext_object_def.instance != MIB_OBJECT_NONE) {
			msg_ps->state = SNMP_MSG_EXTERNAL_GET_VALUE;
			en->get_value_q(request_id, &msg_ps->ext_object_def);
		} else {
			en->get_object_def_pc(request_id, np.ident_len, np.ident);
			/* search failed, object id points to unknown object (nosuchname) */
			snmp_error_response(msg_ps, SNMP_ES_NOSUCHNAME);
		}
	} else if(msg_ps->state == SNMP_MSG_EXTERNAL_GET_VALUE) {
		struct mib_external_node* en;
		struct snmp_varbind* vb;

		/* get_value() answer */
		en = msg_ps->ext_mib_node;

		/* allocate output varbind */
		vb = (struct snmp_varbind*)mem_malloc(sizeof(struct snmp_varbind));
		LWIP_ASSERT("vb != NULL", vb != NULL);

		if(vb != NULL) {
			vb->next = NULL;
			vb->prev = NULL;

			/* move name from invb to outvb */
			vb->ident = msg_ps->vb_ptr->ident;
			vb->ident_len = msg_ps->vb_ptr->ident_len;
			/* ensure this memory is refereced once only */
			msg_ps->vb_ptr->ident = NULL;
			msg_ps->vb_ptr->ident_len = 0;

			vb->value_type = msg_ps->ext_object_def.asn_type;
			vb->value_len =  msg_ps->ext_object_def.v_len;

			if(vb->value_len > 0) {
				vb->value = mem_malloc(vb->value_len);
				LWIP_ASSERT("vb->value != NULL", vb->value != NULL);

				if(vb->value != NULL) {
					en->get_value_a(request_id, &msg_ps->ext_object_def, vb->value_len, vb->value);
					snmp_varbind_tail_add(&msg_ps->outvb, vb);
					/* search again (if vb_idx < msg_ps->invb.count) */
					msg_ps->state = SNMP_MSG_SEARCH_OBJ;
					msg_ps->vb_idx += 1;
				} else {
					en->get_value_pc(request_id, &msg_ps->ext_object_def);
					LWIP_DEBUGF(SNMP_MSG_DEBUG, ("snmp_msg_event: no variable space\n"));
					msg_ps->vb_ptr->ident = vb->ident;
					msg_ps->vb_ptr->ident_len = vb->ident_len;
					mem_free(vb);
					snmp_error_response(msg_ps, SNMP_ES_TOOBIG);
				}
			} else {
				/* vb->value_len == 0, empty value (e.g. empty string) */
				en->get_value_a(request_id, &msg_ps->ext_object_def, 0, NULL);
				vb->value = NULL;
				snmp_varbind_tail_add(&msg_ps->outvb, vb);
				/* search again (if vb_idx < msg_ps->invb.count) */
				msg_ps->state = SNMP_MSG_SEARCH_OBJ;
				msg_ps->vb_idx += 1;
			}
		} else {
			en->get_value_pc(request_id, &msg_ps->ext_object_def);
			LWIP_DEBUGF(SNMP_MSG_DEBUG, ("snmp_msg_event: no outvb space\n"));
			snmp_error_response(msg_ps, SNMP_ES_TOOBIG);
		}
	}

	while((msg_ps->state == SNMP_MSG_SEARCH_OBJ) &&
	        (msg_ps->vb_idx < msg_ps->invb.count)) {
		struct mib_node* mn;
		struct snmp_name_ptr np;

		if(msg_ps->vb_idx == 0) {
			msg_ps->vb_ptr = msg_ps->invb.head;
		} else {
			msg_ps->vb_ptr = msg_ps->vb_ptr->next;
		}

		/** test object identifier for .iso.org.dod.internet prefix */
		if(snmp_iso_prefix_tst(msg_ps->vb_ptr->ident_len,  msg_ps->vb_ptr->ident)) {
			mn = snmp_search_tree((struct mib_node*)&internet, msg_ps->vb_ptr->ident_len - 4,
			                      msg_ps->vb_ptr->ident + 4, &np);

			if(mn != NULL) {
				if(mn->node_type == MIB_NODE_EX) {
					/* external object */
					struct mib_external_node* en = (struct mib_external_node*)mn;

					msg_ps->state = SNMP_MSG_EXTERNAL_GET_OBJDEF;
					/* save en && args in msg_ps!! */
					msg_ps->ext_mib_node = en;
					msg_ps->ext_name_ptr = np;

					en->get_object_def_q(en->addr_inf, request_id, np.ident_len, np.ident);
				} else {
					/* internal object */
					struct obj_def object_def;

					msg_ps->state = SNMP_MSG_INTERNAL_GET_OBJDEF;
					mn->get_object_def(np.ident_len, np.ident, &object_def);

					if(object_def.instance != MIB_OBJECT_NONE) {
						mn = mn;
					} else {
						/* search failed, object id points to unknown object (nosuchname) */
						mn =  NULL;
					}

					if(mn != NULL) {
						struct snmp_varbind* vb;

						msg_ps->state = SNMP_MSG_INTERNAL_GET_VALUE;
						/* allocate output varbind */
						vb = (struct snmp_varbind*)mem_malloc(sizeof(struct snmp_varbind));
						LWIP_ASSERT("vb != NULL", vb != NULL);

						if(vb != NULL) {
							vb->next = NULL;
							vb->prev = NULL;

							/* move name from invb to outvb */
							vb->ident = msg_ps->vb_ptr->ident;
							vb->ident_len = msg_ps->vb_ptr->ident_len;
							/* ensure this memory is refereced once only */
							msg_ps->vb_ptr->ident = NULL;
							msg_ps->vb_ptr->ident_len = 0;

							vb->value_type = object_def.asn_type;
							vb->value_len = object_def.v_len;

							if(vb->value_len > 0) {
								vb->value = mem_malloc(vb->value_len);
								LWIP_ASSERT("vb->value != NULL", vb->value != NULL);

								if(vb->value != NULL) {
									mn->get_value(&object_def, vb->value_len, vb->value);
									snmp_varbind_tail_add(&msg_ps->outvb, vb);
									msg_ps->state = SNMP_MSG_SEARCH_OBJ;
									msg_ps->vb_idx += 1;
								} else {
									LWIP_DEBUGF(SNMP_MSG_DEBUG, ("snmp_msg_event: couldn't allocate variable space\n"));
									msg_ps->vb_ptr->ident = vb->ident;
									msg_ps->vb_ptr->ident_len = vb->ident_len;
									mem_free(vb);
									snmp_error_response(msg_ps, SNMP_ES_TOOBIG);
								}
							} else {
								/* vb->value_len == 0, empty value (e.g. empty string) */
								vb->value = NULL;
								snmp_varbind_tail_add(&msg_ps->outvb, vb);
								msg_ps->state = SNMP_MSG_SEARCH_OBJ;
								msg_ps->vb_idx += 1;
							}
						} else {
							LWIP_DEBUGF(SNMP_MSG_DEBUG, ("snmp_msg_event: couldn't allocate outvb space\n"));
							snmp_error_response(msg_ps, SNMP_ES_TOOBIG);
						}
					}
				}
			}
		} else {
			mn = NULL;
		}

		if(mn == NULL) {
			/* mn == NULL, noSuchName */
			snmp_error_response(msg_ps, SNMP_ES_NOSUCHNAME);
		}
	}

	if((msg_ps->state == SNMP_MSG_SEARCH_OBJ) &&
	        (msg_ps->vb_idx == msg_ps->invb.count)) {
		snmp_ok_response(msg_ps);
	}
}

/**
 * Service an internal or external event for SNMP GETNEXT.
 *
 * @param request_id identifies requests from 0 to (SNMP_CONCURRENT_REQUESTS-1)
 * @param msg_ps points to the assosicated message process state
 */
static void
snmp_msg_getnext_event(u8_t request_id, struct snmp_msg_pstat* msg_ps)
{
	LWIP_DEBUGF(SNMP_MSG_DEBUG, ("snmp_msg_getnext_event: msg_ps->state==%"U16_F"\n", (u16_t)msg_ps->state));

	if(msg_ps->state == SNMP_MSG_EXTERNAL_GET_OBJDEF) {
		struct mib_external_node* en;

		/* get_object_def() answer*/
		en = msg_ps->ext_mib_node;

		/* translate answer into a known lifeform */
		en->get_object_def_a(request_id, 1, &msg_ps->ext_oid.id[msg_ps->ext_oid.len - 1], &msg_ps->ext_object_def);

		if(msg_ps->ext_object_def.instance != MIB_OBJECT_NONE) {
			msg_ps->state = SNMP_MSG_EXTERNAL_GET_VALUE;
			en->get_value_q(request_id, &msg_ps->ext_object_def);
		} else {
			en->get_object_def_pc(request_id, 1, &msg_ps->ext_oid.id[msg_ps->ext_oid.len - 1]);
			/* search failed, object id points to unknown object (nosuchname) */
			snmp_error_response(msg_ps, SNMP_ES_NOSUCHNAME);
		}
	} else if(msg_ps->state == SNMP_MSG_EXTERNAL_GET_VALUE) {
		struct mib_external_node* en;
		struct snmp_varbind* vb;

		/* get_value() answer */
		en = msg_ps->ext_mib_node;

		vb = snmp_varbind_alloc(&msg_ps->ext_oid,
		                        msg_ps->ext_object_def.asn_type,
		                        msg_ps->ext_object_def.v_len);

		if(vb != NULL) {
			en->get_value_a(request_id, &msg_ps->ext_object_def, vb->value_len, vb->value);
			snmp_varbind_tail_add(&msg_ps->outvb, vb);
			msg_ps->state = SNMP_MSG_SEARCH_OBJ;
			msg_ps->vb_idx += 1;
		} else {
			en->get_value_pc(request_id, &msg_ps->ext_object_def);
			LWIP_DEBUGF(SNMP_MSG_DEBUG, ("snmp_msg_getnext_event: couldn't allocate outvb space\n"));
			snmp_error_response(msg_ps, SNMP_ES_TOOBIG);
		}
	}

	while((msg_ps->state == SNMP_MSG_SEARCH_OBJ) &&
	        (msg_ps->vb_idx < msg_ps->invb.count)) {
		struct mib_node* mn;
		struct snmp_obj_id oid;

		if(msg_ps->vb_idx == 0) {
			msg_ps->vb_ptr = msg_ps->invb.head;
		} else {
			msg_ps->vb_ptr = msg_ps->vb_ptr->next;
		}

		if(snmp_iso_prefix_expand(msg_ps->vb_ptr->ident_len, msg_ps->vb_ptr->ident, &oid)) {
			if(msg_ps->vb_ptr->ident_len > 3) {
				/* can offset ident_len and ident */
				mn = snmp_expand_tree((struct mib_node*)&internet,
				                      msg_ps->vb_ptr->ident_len - 4,
				                      msg_ps->vb_ptr->ident + 4, &oid);
			} else {
				/* can't offset ident_len -4, ident + 4 */
				mn = snmp_expand_tree((struct mib_node*)&internet, 0, NULL, &oid);
			}
		} else {
			mn = NULL;
		}

		if(mn != NULL) {
			if(mn->node_type == MIB_NODE_EX) {
				/* external object */
				struct mib_external_node* en = (struct mib_external_node*)mn;

				msg_ps->state = SNMP_MSG_EXTERNAL_GET_OBJDEF;
				/* save en && args in msg_ps!! */
				msg_ps->ext_mib_node = en;
				msg_ps->ext_oid = oid;

				en->get_object_def_q(en->addr_inf, request_id, 1, &oid.id[oid.len - 1]);
			} else {
				/* internal object */
				struct obj_def object_def;
				struct snmp_varbind* vb;

				msg_ps->state = SNMP_MSG_INTERNAL_GET_OBJDEF;
				mn->get_object_def(1, &oid.id[oid.len - 1], &object_def);

				vb = snmp_varbind_alloc(&oid, object_def.asn_type, object_def.v_len);

				if(vb != NULL) {
					msg_ps->state = SNMP_MSG_INTERNAL_GET_VALUE;
					mn->get_value(&object_def, object_def.v_len, vb->value);
					snmp_varbind_tail_add(&msg_ps->outvb, vb);
					msg_ps->state = SNMP_MSG_SEARCH_OBJ;
					msg_ps->vb_idx += 1;
				} else {
					LWIP_DEBUGF(SNMP_MSG_DEBUG, ("snmp_recv couldn't allocate outvb space\n"));
					snmp_error_response(msg_ps, SNMP_ES_TOOBIG);
				}
			}
		}

		if(mn == NULL) {
			/* mn == NULL, noSuchName */
			snmp_error_response(msg_ps, SNMP_ES_NOSUCHNAME);
		}
	}

	if((msg_ps->state == SNMP_MSG_SEARCH_OBJ) &&
	        (msg_ps->vb_idx == msg_ps->invb.count)) {
		snmp_ok_response(msg_ps);
	}
}

/**
 * Service an internal or external event for SNMP SET.
 *
 * @param request_id identifies requests from 0 to (SNMP_CONCURRENT_REQUESTS-1)
 * @param msg_ps points to the assosicated message process state
 */
static void
snmp_msg_set_event(u8_t request_id, struct snmp_msg_pstat* msg_ps)
{
	LWIP_DEBUGF(SNMP_MSG_DEBUG, ("snmp_msg_set_event: msg_ps->state==%"U16_F"\n", (u16_t)msg_ps->state));

	if(msg_ps->state == SNMP_MSG_EXTERNAL_GET_OBJDEF) {
		struct mib_external_node* en;
		struct snmp_name_ptr np;

		/* get_object_def() answer*/
		en = msg_ps->ext_mib_node;
		np = msg_ps->ext_name_ptr;

		/* translate answer into a known lifeform */
		en->get_object_def_a(request_id, np.ident_len, np.ident, &msg_ps->ext_object_def);

		if(msg_ps->ext_object_def.instance != MIB_OBJECT_NONE) {
			msg_ps->state = SNMP_MSG_EXTERNAL_SET_TEST;
			en->set_test_q(request_id, &msg_ps->ext_object_def);
		} else {
			en->get_object_def_pc(request_id, np.ident_len, np.ident);
			/* search failed, object id points to unknown object (nosuchname) */
			snmp_error_response(msg_ps, SNMP_ES_NOSUCHNAME);
		}
	} else if(msg_ps->state == SNMP_MSG_EXTERNAL_SET_TEST) {
		struct mib_external_node* en;

		/* set_test() answer*/
		en = msg_ps->ext_mib_node;

		if(msg_ps->ext_object_def.access == MIB_OBJECT_READ_WRITE) {
			if((msg_ps->ext_object_def.asn_type == msg_ps->vb_ptr->value_type) &&
			        (en->set_test_a(request_id, &msg_ps->ext_object_def,
			                        msg_ps->vb_ptr->value_len, msg_ps->vb_ptr->value) != 0)) {
				msg_ps->state = SNMP_MSG_SEARCH_OBJ;
				msg_ps->vb_idx += 1;
			} else {
				en->set_test_pc(request_id, &msg_ps->ext_object_def);
				/* bad value */
				snmp_error_response(msg_ps, SNMP_ES_BADVALUE);
			}
		} else {
			en->set_test_pc(request_id, &msg_ps->ext_object_def);
			/* object not available for set */
			snmp_error_response(msg_ps, SNMP_ES_NOSUCHNAME);
		}
	} else if(msg_ps->state == SNMP_MSG_EXTERNAL_GET_OBJDEF_S) {
		struct mib_external_node* en;
		struct snmp_name_ptr np;

		/* get_object_def() answer*/
		en = msg_ps->ext_mib_node;
		np = msg_ps->ext_name_ptr;

		/* translate answer into a known lifeform */
		en->get_object_def_a(request_id, np.ident_len, np.ident, &msg_ps->ext_object_def);

		if(msg_ps->ext_object_def.instance != MIB_OBJECT_NONE) {
			msg_ps->state = SNMP_MSG_EXTERNAL_SET_VALUE;
			en->set_value_q(request_id, &msg_ps->ext_object_def,
			                msg_ps->vb_ptr->value_len, msg_ps->vb_ptr->value);
		} else {
			en->get_object_def_pc(request_id, np.ident_len, np.ident);
			/* set_value failed, object has disappeared for some odd reason?? */
			snmp_error_response(msg_ps, SNMP_ES_GENERROR);
		}
	} else if(msg_ps->state == SNMP_MSG_EXTERNAL_SET_VALUE) {
		struct mib_external_node* en;

		/** set_value_a() */
		en = msg_ps->ext_mib_node;
		en->set_value_a(request_id, &msg_ps->ext_object_def,
		                msg_ps->vb_ptr->value_len, msg_ps->vb_ptr->value);

		/** @todo use set_value_pc() if toobig */
		msg_ps->state = SNMP_MSG_INTERNAL_SET_VALUE;
		msg_ps->vb_idx += 1;
	}

	/* test all values before setting */
	while((msg_ps->state == SNMP_MSG_SEARCH_OBJ) &&
	        (msg_ps->vb_idx < msg_ps->invb.count)) {
		struct mib_node* mn;
		struct snmp_name_ptr np;

		if(msg_ps->vb_idx == 0) {
			msg_ps->vb_ptr = msg_ps->invb.head;
		} else {
			msg_ps->vb_ptr = msg_ps->vb_ptr->next;
		}

		/** test object identifier for .iso.org.dod.internet prefix */
		if(snmp_iso_prefix_tst(msg_ps->vb_ptr->ident_len,  msg_ps->vb_ptr->ident)) {
			mn = snmp_search_tree((struct mib_node*)&internet, msg_ps->vb_ptr->ident_len - 4,
			                      msg_ps->vb_ptr->ident + 4, &np);

			if(mn != NULL) {
				if(mn->node_type == MIB_NODE_EX) {
					/* external object */
					struct mib_external_node* en = (struct mib_external_node*)mn;

					msg_ps->state = SNMP_MSG_EXTERNAL_GET_OBJDEF;
					/* save en && args in msg_ps!! */
					msg_ps->ext_mib_node = en;
					msg_ps->ext_name_ptr = np;

					en->get_object_def_q(en->addr_inf, request_id, np.ident_len, np.ident);
				} else {
					/* internal object */
					struct obj_def object_def;

					msg_ps->state = SNMP_MSG_INTERNAL_GET_OBJDEF;
					mn->get_object_def(np.ident_len, np.ident, &object_def);

					if(object_def.instance != MIB_OBJECT_NONE) {
						mn = mn;
					} else {
						/* search failed, object id points to unknown object (nosuchname) */
						mn = NULL;
					}

					if(mn != NULL) {
						msg_ps->state = SNMP_MSG_INTERNAL_SET_TEST;

						if(object_def.access == MIB_OBJECT_READ_WRITE) {
							if((object_def.asn_type == msg_ps->vb_ptr->value_type) &&
							        (mn->set_test(&object_def, msg_ps->vb_ptr->value_len, msg_ps->vb_ptr->value) != 0)) {
								msg_ps->state = SNMP_MSG_SEARCH_OBJ;
								msg_ps->vb_idx += 1;
							} else {
								/* bad value */
								snmp_error_response(msg_ps, SNMP_ES_BADVALUE);
							}
						} else {
							/* object not available for set */
							snmp_error_response(msg_ps, SNMP_ES_NOSUCHNAME);
						}
					}
				}
			}
		} else {
			mn = NULL;
		}

		if(mn == NULL) {
			/* mn == NULL, noSuchName */
			snmp_error_response(msg_ps, SNMP_ES_NOSUCHNAME);
		}
	}

	if((msg_ps->state == SNMP_MSG_SEARCH_OBJ) &&
	        (msg_ps->vb_idx == msg_ps->invb.count)) {
		msg_ps->vb_idx = 0;
		msg_ps->state = SNMP_MSG_INTERNAL_SET_VALUE;
	}

	/* set all values "atomically" (be as "atomic" as possible) */
	while((msg_ps->state == SNMP_MSG_INTERNAL_SET_VALUE) &&
	        (msg_ps->vb_idx < msg_ps->invb.count)) {
		struct mib_node* mn;
		struct snmp_name_ptr np;

		if(msg_ps->vb_idx == 0) {
			msg_ps->vb_ptr = msg_ps->invb.head;
		} else {
			msg_ps->vb_ptr = msg_ps->vb_ptr->next;
		}

		/* skip iso prefix test, was done previously while settesting() */
		mn = snmp_search_tree((struct mib_node*)&internet, msg_ps->vb_ptr->ident_len - 4,
		                      msg_ps->vb_ptr->ident + 4, &np);

		/* check if object is still available
		   (e.g. external hot-plug thingy present?) */
		if(mn != NULL) {
			if(mn->node_type == MIB_NODE_EX) {
				/* external object */
				struct mib_external_node* en = (struct mib_external_node*)mn;

				msg_ps->state = SNMP_MSG_EXTERNAL_GET_OBJDEF_S;
				/* save en && args in msg_ps!! */
				msg_ps->ext_mib_node = en;
				msg_ps->ext_name_ptr = np;

				en->get_object_def_q(en->addr_inf, request_id, np.ident_len, np.ident);
			} else {
				/* internal object */
				struct obj_def object_def;

				msg_ps->state = SNMP_MSG_INTERNAL_GET_OBJDEF_S;
				mn->get_object_def(np.ident_len, np.ident, &object_def);
				msg_ps->state = SNMP_MSG_INTERNAL_SET_VALUE;
				mn->set_value(&object_def, msg_ps->vb_ptr->value_len, msg_ps->vb_ptr->value);
				msg_ps->vb_idx += 1;
			}
		}
	}

	if((msg_ps->state == SNMP_MSG_INTERNAL_SET_VALUE) &&
	        (msg_ps->vb_idx == msg_ps->invb.count)) {
		/* simply echo the input if we can set it
		   @todo do we need to return the actual value?
		   e.g. if value is silently modified or behaves sticky? */
		msg_ps->outvb = msg_ps->invb;
		msg_ps->invb.head = NULL;
		msg_ps->invb.tail = NULL;
		msg_ps->invb.count = 0;
		snmp_ok_response(msg_ps);
	}
}


/**
 * Handle one internal or external event.
 * Called for one async event. (recv external/private answer)
 *
 * @param request_id identifies requests from 0 to (SNMP_CONCURRENT_REQUESTS-1)
 */
void
snmp_msg_event(u8_t request_id)
{
	struct snmp_msg_pstat* msg_ps;

	if(request_id < SNMP_CONCURRENT_REQUESTS) {
		msg_ps = &msg_input_list[request_id];

		if(msg_ps->rt == SNMP_ASN1_PDU_GET_NEXT_REQ) {
			snmp_msg_getnext_event(request_id, msg_ps);
		} else if(msg_ps->rt == SNMP_ASN1_PDU_GET_REQ) {
			snmp_msg_get_event(request_id, msg_ps);
		} else if(msg_ps->rt == SNMP_ASN1_PDU_SET_REQ) {
			snmp_msg_set_event(request_id, msg_ps);
		}
	}
}


/* lwIP UDP receive callback function */
static void
snmp_recv(void* arg, struct udp_pcb* pcb, struct pbuf* p, struct ip_addr* addr, u16_t port)
{
	struct udp_hdr* udphdr;

	/* suppress unused argument warning */
	LWIP_UNUSED_ARG(arg);

	/* peek in the UDP header (goto IP payload) */
	if(pbuf_header(p, UDP_HLEN)) {
		LWIP_ASSERT("Can't move to UDP header", 0);
		pbuf_free(p);
		return;
	}

	udphdr = p->payload;

	/* check if datagram is really directed at us (including broadcast requests) */
	if((pcb == snmp1_pcb) && (ntohs(udphdr->dest) == SNMP_IN_PORT)) {
		struct snmp_msg_pstat* msg_ps;
		u8_t req_idx;

		/* traverse input message process list, look for SNMP_MSG_EMPTY */
		msg_ps = &msg_input_list[0];
		req_idx = 0;

		while((req_idx < SNMP_CONCURRENT_REQUESTS) && (msg_ps->state != SNMP_MSG_EMPTY)) {
			req_idx++;
			msg_ps++;
		}

		if(req_idx != SNMP_CONCURRENT_REQUESTS) {
			err_t err_ret;
			u16_t payload_len;
			u16_t payload_ofs;
			u16_t varbind_ofs = 0;

			/* accepting request */
			snmp_inc_snmpinpkts();
			/* record used 'protocol control block' */
			msg_ps->pcb = pcb;
			/* source address (network order) */
			msg_ps->sip = *addr;
			/* source port (host order (lwIP oddity)) */
			msg_ps->sp = port;
			/* read UDP payload length from UDP header */
			payload_len = ntohs(udphdr->len) - UDP_HLEN;

			/* adjust to UDP payload */
			payload_ofs = UDP_HLEN;

			/* check total length, version, community, pdu type */
			err_ret = snmp_pdu_header_check(p, payload_ofs, payload_len, &varbind_ofs, msg_ps);

			if(((msg_ps->rt == SNMP_ASN1_PDU_GET_REQ) ||
			        (msg_ps->rt == SNMP_ASN1_PDU_GET_NEXT_REQ) ||
			        (msg_ps->rt == SNMP_ASN1_PDU_SET_REQ)) &&
			        ((msg_ps->error_status == SNMP_ES_NOERROR) &&
			         (msg_ps->error_index == 0))) {
				/* Only accept requests and requests without error (be robust) */
				err_ret = err_ret;
			} else {
				/* Reject response and trap headers or error requests as input! */
				err_ret = ERR_ARG;
			}

			if(err_ret == ERR_OK) {
				LWIP_DEBUGF(SNMP_MSG_DEBUG, ("snmp_recv ok, community %s\n", msg_ps->community));

				/* Builds a list of variable bindings. Copy the varbinds from the pbuf
				  chain to glue them when these are divided over two or more pbuf's. */
				err_ret = snmp_pdu_dec_varbindlist(p, varbind_ofs, &varbind_ofs, msg_ps);

				if((err_ret == ERR_OK) && (msg_ps->invb.count > 0)) {
					/* we've decoded the incoming message, release input msg now */
					pbuf_free(p);

					msg_ps->error_status = SNMP_ES_NOERROR;
					msg_ps->error_index = 0;
					/* find object for each variable binding */
					msg_ps->state = SNMP_MSG_SEARCH_OBJ;
					/* first variable binding from list to inspect */
					msg_ps->vb_idx = 0;

					LWIP_DEBUGF(SNMP_MSG_DEBUG, ("snmp_recv varbind cnt=%"U16_F"\n", (u16_t)msg_ps->invb.count));

					/* handle input event and as much objects as possible in one go */
					snmp_msg_event(req_idx);
				} else {
					/* varbind-list decode failed, or varbind list empty.
					   drop request silently, do not return error!
					   (errors are only returned for a specific varbind failure) */
					pbuf_free(p);
					LWIP_DEBUGF(SNMP_MSG_DEBUG, ("snmp_pdu_dec_varbindlist() failed\n"));
				}
			} else {
				/* header check failed
				   drop request silently, do not return error! */
				pbuf_free(p);
				LWIP_DEBUGF(SNMP_MSG_DEBUG, ("snmp_pdu_header_check() failed\n"));
			}
		} else {
			/* exceeding number of concurrent requests */
			pbuf_free(p);
		}
	} else {
		/* datagram not for us */
		pbuf_free(p);
	}
}

/**
 * Checks and decodes incoming SNMP message header, logs header errors.
 *
 * @param p points to pbuf chain of SNMP message (UDP payload)
 * @param ofs points to first octet of SNMP message
 * @param pdu_len the length of the UDP payload
 * @param ofs_ret returns the ofset of the variable bindings
 * @param m_stat points to the current message request state return
 * @return
 * - ERR_OK SNMP header is sane and accepted
 * - ERR_ARG SNMP header is either malformed or rejected
 */
static err_t
snmp_pdu_header_check(struct pbuf* p, u16_t ofs, u16_t pdu_len, u16_t* ofs_ret, struct snmp_msg_pstat* m_stat)
{
	err_t derr;
	u16_t len, ofs_base;
	u8_t  len_octets;
	u8_t  type;
	s32_t version;

	ofs_base = ofs;
	snmp_asn1_dec_type(p, ofs, &type);
	derr = snmp_asn1_dec_length(p, ofs + 1, &len_octets, &len);

	if((derr != ERR_OK) ||
	        (pdu_len != (1 + len_octets + len)) ||
	        (type != (SNMP_ASN1_UNIV | SNMP_ASN1_CONSTR | SNMP_ASN1_SEQ))) {
		snmp_inc_snmpinasnparseerrs();
		return ERR_ARG;
	}

	ofs += (1 + len_octets);
	snmp_asn1_dec_type(p, ofs, &type);
	derr = snmp_asn1_dec_length(p, ofs + 1, &len_octets, &len);

	if((derr != ERR_OK) || (type != (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_INTEG))) {
		/* can't decode or no integer (version) */
		snmp_inc_snmpinasnparseerrs();
		return ERR_ARG;
	}

	derr = snmp_asn1_dec_s32t(p, ofs + 1 + len_octets, len, &version);

	if(derr != ERR_OK) {
		/* can't decode */
		snmp_inc_snmpinasnparseerrs();
		return ERR_ARG;
	}

	if(version != 0) {
		/* not version 1 */
		snmp_inc_snmpinbadversions();
		return ERR_ARG;
	}

	ofs += (1 + len_octets + len);
	snmp_asn1_dec_type(p, ofs, &type);
	derr = snmp_asn1_dec_length(p, ofs + 1, &len_octets, &len);

	if((derr != ERR_OK) || (type != (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_OC_STR))) {
		/* can't decode or no octet string (community) */
		snmp_inc_snmpinasnparseerrs();
		return ERR_ARG;
	}

	derr = snmp_asn1_dec_raw(p, ofs + 1 + len_octets, len, SNMP_COMMUNITY_STR_LEN, m_stat->community);

	if(derr != ERR_OK) {
		snmp_inc_snmpinasnparseerrs();
		return ERR_ARG;
	}

	/* add zero terminator */
	len = ((len < (SNMP_COMMUNITY_STR_LEN)) ? (len) : (SNMP_COMMUNITY_STR_LEN));
	m_stat->community[len] = 0;
	m_stat->com_strlen = len;

	if(strncmp(snmp_publiccommunity, (const char*)m_stat->community, SNMP_COMMUNITY_STR_LEN) != 0) {
		/** @todo: move this if we need to check more names */
		snmp_inc_snmpinbadcommunitynames();
		snmp_authfail_trap();
		return ERR_ARG;
	}

	ofs += (1 + len_octets + len);
	snmp_asn1_dec_type(p, ofs, &type);
	derr = snmp_asn1_dec_length(p, ofs + 1, &len_octets, &len);

	if(derr != ERR_OK) {
		snmp_inc_snmpinasnparseerrs();
		return ERR_ARG;
	}

	switch(type) {
		case(SNMP_ASN1_CONTXT | SNMP_ASN1_CONSTR | SNMP_ASN1_PDU_GET_REQ):
			/* GetRequest PDU */
			snmp_inc_snmpingetrequests();
			derr = ERR_OK;
			break;

		case(SNMP_ASN1_CONTXT | SNMP_ASN1_CONSTR | SNMP_ASN1_PDU_GET_NEXT_REQ):
			/* GetNextRequest PDU */
			snmp_inc_snmpingetnexts();
			derr = ERR_OK;
			break;

		case(SNMP_ASN1_CONTXT | SNMP_ASN1_CONSTR | SNMP_ASN1_PDU_GET_RESP):
			/* GetResponse PDU */
			snmp_inc_snmpingetresponses();
			derr = ERR_ARG;
			break;

		case(SNMP_ASN1_CONTXT | SNMP_ASN1_CONSTR | SNMP_ASN1_PDU_SET_REQ):
			/* SetRequest PDU */
			snmp_inc_snmpinsetrequests();
			derr = ERR_OK;
			break;

		case(SNMP_ASN1_CONTXT | SNMP_ASN1_CONSTR | SNMP_ASN1_PDU_TRAP):
			/* Trap PDU */
			snmp_inc_snmpintraps();
			derr = ERR_ARG;
			break;

		default:
			snmp_inc_snmpinasnparseerrs();
			derr = ERR_ARG;
			break;
	}

	if(derr != ERR_OK) {
		/* unsupported input PDU for this agent (no parse error) */
		return ERR_ARG;
	}

	m_stat->rt = type & 0x1F;
	ofs += (1 + len_octets);

	if(len != (pdu_len - (ofs - ofs_base))) {
		/* decoded PDU length does not equal actual payload length */
		snmp_inc_snmpinasnparseerrs();
		return ERR_ARG;
	}

	snmp_asn1_dec_type(p, ofs, &type);
	derr = snmp_asn1_dec_length(p, ofs + 1, &len_octets, &len);

	if((derr != ERR_OK) || (type != (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_INTEG))) {
		/* can't decode or no integer (request ID) */
		snmp_inc_snmpinasnparseerrs();
		return ERR_ARG;
	}

	derr = snmp_asn1_dec_s32t(p, ofs + 1 + len_octets, len, &m_stat->rid);

	if(derr != ERR_OK) {
		/* can't decode */
		snmp_inc_snmpinasnparseerrs();
		return ERR_ARG;
	}

	ofs += (1 + len_octets + len);
	snmp_asn1_dec_type(p, ofs, &type);
	derr = snmp_asn1_dec_length(p, ofs + 1, &len_octets, &len);

	if((derr != ERR_OK) || (type != (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_INTEG))) {
		/* can't decode or no integer (error-status) */
		snmp_inc_snmpinasnparseerrs();
		return ERR_ARG;
	}

	/* must be noError (0) for incoming requests.
	   log errors for mib-2 completeness and for debug purposes */
	derr = snmp_asn1_dec_s32t(p, ofs + 1 + len_octets, len, &m_stat->error_status);

	if(derr != ERR_OK) {
		/* can't decode */
		snmp_inc_snmpinasnparseerrs();
		return ERR_ARG;
	}

	switch(m_stat->error_status) {
		case SNMP_ES_TOOBIG:
			snmp_inc_snmpintoobigs();
			break;

		case SNMP_ES_NOSUCHNAME:
			snmp_inc_snmpinnosuchnames();
			break;

		case SNMP_ES_BADVALUE:
			snmp_inc_snmpinbadvalues();
			break;

		case SNMP_ES_READONLY:
			snmp_inc_snmpinreadonlys();
			break;

		case SNMP_ES_GENERROR:
			snmp_inc_snmpingenerrs();
			break;
	}

	ofs += (1 + len_octets + len);
	snmp_asn1_dec_type(p, ofs, &type);
	derr = snmp_asn1_dec_length(p, ofs + 1, &len_octets, &len);

	if((derr != ERR_OK) || (type != (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_INTEG))) {
		/* can't decode or no integer (error-index) */
		snmp_inc_snmpinasnparseerrs();
		return ERR_ARG;
	}

	/* must be 0 for incoming requests.
	   decode anyway to catch bad integers (and dirty tricks) */
	derr = snmp_asn1_dec_s32t(p, ofs + 1 + len_octets, len, &m_stat->error_index);

	if(derr != ERR_OK) {
		/* can't decode */
		snmp_inc_snmpinasnparseerrs();
		return ERR_ARG;
	}

	ofs += (1 + len_octets + len);
	*ofs_ret = ofs;
	return ERR_OK;
}

static err_t
snmp_pdu_dec_varbindlist(struct pbuf* p, u16_t ofs, u16_t* ofs_ret, struct snmp_msg_pstat* m_stat)
{
	err_t derr;
	u16_t len, vb_len;
	u8_t  len_octets;
	u8_t type;

	/* variable binding list */
	snmp_asn1_dec_type(p, ofs, &type);
	derr = snmp_asn1_dec_length(p, ofs + 1, &len_octets, &vb_len);

	if((derr != ERR_OK) ||
	        (type != (SNMP_ASN1_UNIV | SNMP_ASN1_CONSTR | SNMP_ASN1_SEQ))) {
		snmp_inc_snmpinasnparseerrs();
		return ERR_ARG;
	}

	ofs += (1 + len_octets);

	/* start with empty list */
	m_stat->invb.count = 0;
	m_stat->invb.head = NULL;
	m_stat->invb.tail = NULL;

	while(vb_len > 0) {
		struct snmp_obj_id oid, oid_value;
		struct snmp_varbind* vb;

		snmp_asn1_dec_type(p, ofs, &type);
		derr = snmp_asn1_dec_length(p, ofs + 1, &len_octets, &len);

		if((derr != ERR_OK) ||
		        (type != (SNMP_ASN1_UNIV | SNMP_ASN1_CONSTR | SNMP_ASN1_SEQ)) ||
		        (len == 0) || (len > vb_len)) {
			snmp_inc_snmpinasnparseerrs();
			/* free varbinds (if available) */
			snmp_varbind_list_free(&m_stat->invb);
			return ERR_ARG;
		}

		ofs += (1 + len_octets);
		vb_len -= (1 + len_octets);

		snmp_asn1_dec_type(p, ofs, &type);
		derr = snmp_asn1_dec_length(p, ofs + 1, &len_octets, &len);

		if((derr != ERR_OK) || (type != (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_OBJ_ID))) {
			/* can't decode object name length */
			snmp_inc_snmpinasnparseerrs();
			/* free varbinds (if available) */
			snmp_varbind_list_free(&m_stat->invb);
			return ERR_ARG;
		}

		derr = snmp_asn1_dec_oid(p, ofs + 1 + len_octets, len, &oid);

		if(derr != ERR_OK) {
			/* can't decode object name */
			snmp_inc_snmpinasnparseerrs();
			/* free varbinds (if available) */
			snmp_varbind_list_free(&m_stat->invb);
			return ERR_ARG;
		}

		ofs += (1 + len_octets + len);
		vb_len -= (1 + len_octets + len);

		snmp_asn1_dec_type(p, ofs, &type);
		derr = snmp_asn1_dec_length(p, ofs + 1, &len_octets, &len);

		if(derr != ERR_OK) {
			/* can't decode object value length */
			snmp_inc_snmpinasnparseerrs();
			/* free varbinds (if available) */
			snmp_varbind_list_free(&m_stat->invb);
			return ERR_ARG;
		}

		switch(type) {
			case(SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_INTEG):
				vb = snmp_varbind_alloc(&oid, type, sizeof(s32_t));

				if(vb != NULL) {
					s32_t* vptr = vb->value;

					derr = snmp_asn1_dec_s32t(p, ofs + 1 + len_octets, len, vptr);
					snmp_varbind_tail_add(&m_stat->invb, vb);
				} else {
					derr = ERR_ARG;
				}

				break;

			case(SNMP_ASN1_APPLIC | SNMP_ASN1_PRIMIT | SNMP_ASN1_COUNTER):
			case(SNMP_ASN1_APPLIC | SNMP_ASN1_PRIMIT | SNMP_ASN1_GAUGE):
			case(SNMP_ASN1_APPLIC | SNMP_ASN1_PRIMIT | SNMP_ASN1_TIMETICKS):
				vb = snmp_varbind_alloc(&oid, type, sizeof(u32_t));

				if(vb != NULL) {
					u32_t* vptr = vb->value;

					derr = snmp_asn1_dec_u32t(p, ofs + 1 + len_octets, len, vptr);
					snmp_varbind_tail_add(&m_stat->invb, vb);
				} else {
					derr = ERR_ARG;
				}

				break;

			case(SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_OC_STR):
			case(SNMP_ASN1_APPLIC | SNMP_ASN1_PRIMIT | SNMP_ASN1_OPAQUE):
				vb = snmp_varbind_alloc(&oid, type, len);

				if(vb != NULL) {
					derr = snmp_asn1_dec_raw(p, ofs + 1 + len_octets, len, vb->value_len, vb->value);
					snmp_varbind_tail_add(&m_stat->invb, vb);
				} else {
					derr = ERR_ARG;
				}

				break;

			case(SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_NUL):
				vb = snmp_varbind_alloc(&oid, type, 0);

				if(vb != NULL) {
					snmp_varbind_tail_add(&m_stat->invb, vb);
					derr = ERR_OK;
				} else {
					derr = ERR_ARG;
				}

				break;

			case(SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_OBJ_ID):
				derr = snmp_asn1_dec_oid(p, ofs + 1 + len_octets, len, &oid_value);

				if(derr == ERR_OK) {
					vb = snmp_varbind_alloc(&oid, type, oid_value.len * sizeof(s32_t));

					if(vb != NULL) {
						u8_t i = oid_value.len;
						s32_t* vptr = vb->value;

						while(i > 0) {
							i--;
							vptr[i] = oid_value.id[i];
						}

						snmp_varbind_tail_add(&m_stat->invb, vb);
						derr = ERR_OK;
					} else {
						derr = ERR_ARG;
					}
				}

				break;

			case(SNMP_ASN1_APPLIC | SNMP_ASN1_PRIMIT | SNMP_ASN1_IPADDR):
				if(len == 4) {
					/* must be exactly 4 octets! */
					vb = snmp_varbind_alloc(&oid, type, 4);

					if(vb != NULL) {
						derr = snmp_asn1_dec_raw(p, ofs + 1 + len_octets, len, vb->value_len, vb->value);
						snmp_varbind_tail_add(&m_stat->invb, vb);
					} else {
						derr = ERR_ARG;
					}
				} else {
					derr = ERR_ARG;
				}

				break;

			default:
				derr = ERR_ARG;
				break;
		}

		if(derr != ERR_OK) {
			snmp_inc_snmpinasnparseerrs();
			/* free varbinds (if available) */
			snmp_varbind_list_free(&m_stat->invb);
			return ERR_ARG;
		}

		ofs += (1 + len_octets + len);
		vb_len -= (1 + len_octets + len);
	}

	if(m_stat->rt == SNMP_ASN1_PDU_SET_REQ) {
		snmp_add_snmpintotalsetvars(m_stat->invb.count);
	} else {
		snmp_add_snmpintotalreqvars(m_stat->invb.count);
	}

	*ofs_ret = ofs;
	return ERR_OK;
}

struct snmp_varbind*
snmp_varbind_alloc(struct snmp_obj_id* oid, u8_t type, u8_t len)
{
	struct snmp_varbind* vb;

	vb = (struct snmp_varbind*)mem_malloc(sizeof(struct snmp_varbind));
	LWIP_ASSERT("vb != NULL", vb != NULL);

	if(vb != NULL) {
		u8_t i;

		vb->next = NULL;
		vb->prev = NULL;
		i = oid->len;
		vb->ident_len = i;

		if(i > 0) {
			/* allocate array of s32_t for our object identifier */
			vb->ident = (s32_t*)mem_malloc(sizeof(s32_t) * i);
			LWIP_ASSERT("vb->ident != NULL", vb->ident != NULL);

			if(vb->ident == NULL) {
				mem_free(vb);
				return NULL;
			}

			while(i > 0) {
				i--;
				vb->ident[i] = oid->id[i];
			}
		} else {
			/* i == 0, pass zero length object identifier */
			vb->ident = NULL;
		}

		vb->value_type = type;
		vb->value_len = len;

		if(len > 0) {
			/* allocate raw bytes for our object value */
			vb->value = mem_malloc(len);
			LWIP_ASSERT("vb->value != NULL", vb->value != NULL);

			if(vb->value == NULL) {
				if(vb->ident != NULL) {
					mem_free(vb->ident);
				}

				mem_free(vb);
				return NULL;
			}
		} else {
			/* ASN1_NUL type, or zero length ASN1_OC_STR */
			vb->value = NULL;
		}
	}

	return vb;
}

void
snmp_varbind_free(struct snmp_varbind* vb)
{
	if(vb->value != NULL) {
		mem_free(vb->value);
	}

	if(vb->ident != NULL) {
		mem_free(vb->ident);
	}

	mem_free(vb);
}

void
snmp_varbind_list_free(struct snmp_varbind_root* root)
{
	struct snmp_varbind* vb, *prev;

	vb = root->tail;

	while(vb != NULL) {
		prev = vb->prev;
		snmp_varbind_free(vb);
		vb = prev;
	}

	root->count = 0;
	root->head = NULL;
	root->tail = NULL;
}

void
snmp_varbind_tail_add(struct snmp_varbind_root* root, struct snmp_varbind* vb)
{
	if(root->count == 0) {
		/* add first varbind to list */
		root->head = vb;
		root->tail = vb;
	} else {
		/* add nth varbind to list tail */
		root->tail->next = vb;
		vb->prev = root->tail;
		root->tail = vb;
	}

	root->count += 1;
}

struct snmp_varbind*
snmp_varbind_tail_remove(struct snmp_varbind_root* root)
{
	struct snmp_varbind* vb;

	if(root->count > 0) {
		/* remove tail varbind */
		vb = root->tail;
		root->tail = vb->prev;
		vb->prev->next = NULL;
		root->count -= 1;
	} else {
		/* nothing to remove */
		vb = NULL;
	}

	return vb;
}

#endif /* LWIP_SNMP */
